JPH0414319B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a fuel pin breakage detection method that enables accurate estimation of the scale of fuel pin breakage in a fast breeder reactor (hereinafter referred to as "FBR"), and its method. It relates to an apparatus for carrying out the method.

[Technical background of the invention and its problems]

Nuclear reactors are operated with sufficient safety in mind and the usable time of the fuel pins loaded in the reactor core is limited. However, in the unlikely event that a fuel pin breaks during operation, the coolant will be depleted. This may change the flow, disrupting the thermal balance of the nuclear fuel assembly and even the reactor core, and potentially interfering with reactor operation. Therefore, it is necessary to constantly monitor whether or not the fuel pin is damaged by some means.

By the way, in the case of an FBR, if the fuel pin is damaged during operation, the fission products (hereinafter abbreviated as "FP") generated inside the fuel pin will be released into the liquid sodium coolant. It will be released. Most of these FPs are radioactive substances, and due to their nature, rare gas FPs (Kr, Xe, etc.)
It is broadly classified into volatile FP (Br, Rb, Te, I, Cs, etc.) and non-volatile FP (Sr, Y, Zr, Ru, Ba, La, Ce, etc.). Utilizing this phenomenon, one of the above-mentioned FPs can be used to detect fuel pin breakage in conventional FBRs.
The DN detection method detects delayed neutrons (DN) emitted by some volatile FP nuclides such as Br and I, and the rare gas FP released into the cover gas after being released into the coolant. A method for detecting gamma rays produced by a gamma ray detector, and a method for detecting gamma rays produced by radioactive decay of rare gas FP.
The precipitator method, which electrically collects ionic nuclides such as Rb and Cs and detects the β rays emitted by those nuclides, has been adopted. Using these detection methods, when it is determined that the fuel pin is damaged, the FBR operation can be stopped and the damaged fuel replaced.

However, the conventional detection method described above has the following problems.

In other words, there are different degrees of damage to the fuel pin, ranging from a small case in which a pinhole has occurred to a large case in which the cladding has melted. Generally, if a fuel pin has a small break like a pinhole, only rare gases and volatile FP will be released, but if the break becomes large enough, coolant will leak into the pin from the break. invade and catalyze directly with fuel,
Alternatively, some of the fuel may jump out from the pin breakage into the coolant flow path outside the pin and come into direct contact with the coolant, causing even non-volatile FP, which has almost no solubility in the coolant, to be absorbed into the coolant. released inside. and,
In the case of damage to the size of a pinhole, the damage often does not become more extensive because it does not change the flow of the coolant and has little thermal effect.

However, traditional detection methods detect noble gases and volatile
Since FP radiation is used to detect fuel damage, when fuel damage is detected, it is necessary to scram the reactor and replace the damaged fuel, which is a time-consuming process regardless of the scale of the damage. Of course, it is desirable for a nuclear reactor to operate without fuel damage, but even if a small-scale fuel failure occurs and rare gases and volatile FP are released into the coolant, these FP has many nuclides with short half-lives and is easily transferred to the cover gas system, and radioactive FP can be separated in the exhaust gas treatment system of the cover gas system, so no radioactive substances are released into the environment. Therefore, considering the economic efficiency of nuclear reactor operation, it is desirable to continue operating the reactor in the case of small-scale damage such as a pinhole. Rather,
A serious case for the operation of a nuclear reactor is when a large-scale failure of a fuel pin releases non-volatile FP, which tends to be deposited inside the plant, into the coolant, contaminating the plant. Replacement is required. Therefore, there is a fuel damage detection method that can accurately estimate the scale of fuel damage and accurately determine whether or not it is necessary to replace the damaged fuel, which is economically disadvantageous due to a large amount of effort and prolonged shutdown of the reactor. The reality is that it is hoped that the emergence of

Therefore, in response to such a request, it may be possible to estimate the scale of fuel pin damage by detecting the radiation dose of nonvolatile FP released into the coolant. However, in FBRs, the sodium coolant normally contains a large amount of ²⁴ Na, which has strong radioactivity after being irradiated with high-density neutrons near the reactor core. For this reason, the radioactivity of nonvolatile FP in sodium was buried under the radioactivity of ²⁴ Na, resulting in a problem that accurate detection was almost impossible.

[Object of the present invention]

The present invention was made based on the above circumstances, and its purpose is to accurately estimate the scale of fuel pin damage without causing any hindrance to the operation of the nuclear reactor, and to improve the operation of the nuclear reactor. Provides a method for detecting fuel pin damage, which can contribute to accurate judgment of the continuity of nuclear reactors, the necessity of replacing damaged fuel, and the operation of a nuclear reactor with excellent economic efficiency, and a device for implementing the method. It's about doing.

[Summary of the invention]

In the detection method according to the present invention, a portion of the liquid metal coolant passing through the core of a nuclear reactor is primarily non-volatile.
After passing the flow through a capture device containing a capture member that captures FP, the capture member and the liquid metal coolant are separated, and then the non-volatile FP captured by the capture member is released. The system is characterized by estimating the scale of fuel pin damage by measuring the radiation dose.

That is, the present invention focuses on the fact that non-volatile FP released into liquid metal is easily adsorbed by a specific member, and allows the member to capture non-volatile FP, and after separating the liquid metal from this member. , the amount of radiation emitted from the nonvolatile FP captured in this member is measured.

Further, the detection device according to the present invention is installed in a bypass flow path provided in a primary coolant circulation path of a nuclear reactor that uses liquid metal as a primary coolant, and is inserted in series with this bypass flow path, and mainly contains non-volatile metal. sex
a capture device that accommodates a capture member that captures FP; a means for causing the liquid metal to flow through the capture device for a predetermined period of time; means for separating the remaining liquid metal from the capture member;
and means for measuring the radiation dose emitted by the non-volatile FP captured in the capture member separated from the liquid metal by this means, and estimating the scale of damage to the fuel pin from the radiation dose. It is characterized by the fact that

〔Effect of the invention〕

In the detection method according to the present invention, when the scale of damage to the fuel pin exceeds the size of a pinhole, the fuel pin mixes into the liquid metal that is the coolant, has almost no solubility in the coolant, and is reduced by half. The detection target is non-volatile FP with a long shelf life. During actual detection, a portion of the liquid metal coolant that has passed through the reactor core is passed through a capture device containing a capture member that primarily captures non-volatile FPs for a predetermined period of time. Non-volatile FP material
can be concentrated and accumulated. After that, the capture member and the liquid metal are separated and the amount of radiation emitted by the accumulated non-volatile FP is measured in this state, so it is not affected by the background such as ²⁴ Na. It is possible to measure the radiation dose from non-volatile FP with high sensitivity and estimate the amount of non-volatile FP in liquid metal with high accuracy. Furthermore, since this method detects non-volatile FPs with a long half-life, it is possible to measure radiation doses in locations where there is little influence from neutrons leaking from the reactor core.

Therefore, with this detection method, the scale of damage to the fuel pin can be accurately detected without affecting the operation of the reactor, so the number of times the reactor is scrammed can be reduced. The economic efficiency of nuclear reactor operation can be improved without compromising safety.

Further, the detection device according to the present invention can completely automate the above-mentioned functions, so it can contribute to more efficient operation of the nuclear reactor.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a case where the first embodiment of the present invention is applied.
This is a diagram schematically showing an FBR plant, and 1 in the diagram.
is the reactor vessel. A reactor core 2 is housed inside this reactor vessel 1 . This reactor core 2 is cooled by liquid sodium Q contained inside the reactor main vessel 1. The upper and lower parts of the inside of the reactor vessel 1 are communicated by a primary cooling system piping 3, and liquid sodium Q is transferred from the upper part of the reactor core 2 to the lower part of the reactor core 2 via this primary cooling system piping 3. That's what I do. The primary cooling system piping 3 is provided with an intermediate heat exchanger 4 for discharging the heat of the liquid sodium Q, and a pump 5 for circulating the liquid sodium Q. Note that R in the figure is a cover gas filled in the upper space of the liquid sodium Q.

A bypass passage 6 is provided in the primary cooling system piping 3 on the outlet side from the reactor vessel 1 to the intermediate heat exchanger 4 . In this bypass flow path 6,
An FP detection system 7 is installed.

Specifically, the FP detection system 7 is as shown in FIG.
It is configured as a non-volatile FP detection system.

That is, the bypass channel 6 is provided with the FP capture device 11. This FP capture device 11 is
For example, it is composed of a stainless steel pipe covered with a shielding material such as lead, and in the process of flowing liquid sodium Q inside, the non-volatile FP contained in the liquid sodium Q is removed from the inner surface of the FP capture device 11. It was designed to be deposited in

Bypass channel 6a on the upstream side of the FP capture device 11
Valves 12 and 13 are provided in the downstream side bypass flow path 6b, respectively. Also, valve 1
In the downstream bypass flow path 6b where 3 is provided,
A pump 14 for circulating liquid sodium Q is provided inside the FP capture device 11.

The upstream side of the FP capture device 11 communicates via a valve 15 with a tank 16 that stores liquid sodium. On the other hand, on the downstream side of the FP capture device 11, the valve 1
It communicates with a gas cylinder 18 filled with a cover gas S such as argon gas or nitrogen gas through a valve 19, and a vacuum pump 2 through a valve 19.
Connected to 0.

In addition, in the vicinity of the FP capture device 11, there is a gamma ray detector 2, which is covered with lead or the like on the outside and detects gamma rays from radioactive substances remaining inside the FP capture device 11.
1 is installed.

The operation of the nonvolatile FP detection system 7 configured as described above will be explained.

It is now assumed that liquid sodium Q is being circulated through the primary cooling system piping 3 of the nuclear reactor. If a fuel pin (not shown) housed inside the core 2 is damaged in this state, the above-mentioned rare gas FP and volatile FP will be released into the liquid sodium Q, and if the damage becomes large-scale, non-volatile FP will be released. is released. These FPs circulate within the primary cooling system piping 3 as the liquid sodium Q moves.

When the valves 12 and 13 of the bypass passage 6 are opened and the pump 14 is operated, liquid sodium Q flows into the bypass passage 6. As a result, liquid sodium Q flows through the inside of the FP capture device 11.
When the liquid sodium Q contains nonvolatile FP, the nonvolatile FP is deposited inside the FP capture device 11 by flowing the liquid sodium Q for a predetermined period of time. The amount of this deposit depends on the amount of non-volatile FP contained in the liquid sodium, that is, the amount that depends on the scale of the fuel pin breakage.

After a predetermined period of time has elapsed, the valves 12 and 13 are closed and the valves 15 and 17 are opened, and the cover gas S filled in the gas cylinder 18 is supplied into the FP capture device 11. As a result, the liquid sodium Q contained within the FP capture device 11 is discharged into the tank 16. Therefore, only non-volatile FP remains inside the FP capture device 11, as described above. Therefore, the amount of gamma rays emitted from this remaining nonvolatile FP is measured by the gamma ray detector 21.

When the measurement is completed, close valves 15 and 17, and close valve 1.
9 is opened to operate the vacuum pump 20. As a result, the cover gas S filled inside the FP capture device 11 is evacuated and guided to an exhaust gas treatment system (not shown). After this exhaustion is finished, the valve 19 is closed, the valves 12 and 13 are opened again, and the FP capture device 1 is closed.
Liquid sodium Q is introduced into 1.

By repeating the above procedure, nonvolatile FP can be detected in substantially real time.

Due to the behavior of FP in sodium, non-volatile FP such as Sr and Ba are very likely to deposit on stainless steel piping, and the rate of this deposition increases as the temperature of sodium increases. The detection system 7 is installed in the primary cooling system piping 3 on the exit side of the reactor where the temperature of the liquid sodium Q is high, and the FP capture device 11 is made of stainless steel. Therefore, when nonvolatile FP is contained in the liquid sodium Q, the nonvolatile FP is quickly and efficiently deposited on the inner surface of the FP capture device 11. ^In this case, since the detection target is non-volatile FP with a long half-life, the non-volatile FP detection system 7 can be placed in a position that is not affected by the radioactivity from the reactor core. Since the sodium contained therein is discharged into the tank 16, the FP capture device 11 can measure the gamma rays emitted only from non-volatile FP, which most faithfully indicates the scale of damage to the fuel pin, with extremely high precision. can do.

In addition, as a method for detecting this gamma ray,
The best method is to detect ⁹⁴ Sr, which emits 1428.3 keV gamma rays. In this case, ⁵⁴ Mn and radioactive corrosion products (hereinafter referred to as "CP") contained in sodium and deposited on the stainless steel surface.
The energy of the γ-rays emitted from ⁹⁴ Sr is sufficiently higher than that of ⁶⁰ Co, so
Extremely sensitive measurements of CP gamma rays are possible without interference from Compton. In addition to the above ⁹⁴ Sr, ⁹¹ Sr, ⁹² Sr, ⁹³ Sr, ¹⁰¹ Tc,
γ of ¹⁴¹ Ba, ¹⁴² Ba, ¹⁴³ Ba, ¹⁴⁰ La, ¹⁴² La, etc.
It may be configured to detect lines.

[Other embodiments of the invention]

Note that the nonvolatile FP detection system may be configured as follows.

That is, FIG. 3 is a diagram showing a nonvolatile FP detection system according to a second embodiment of the present invention.

In this example, there are a plurality of
FP capture devices 31, 32, 33, 34, ... are connected in parallel, and valves 41a, 41b, 42a, 42b, 4
By opening and closing operations of 3a, 43b, 44a, 44b,..., liquid sodium Q is made to flow through these FP capture devices 31, 32,... sequentially, and the procedure of the above-mentioned embodiment is performed continuously for each FP capture device. I have to.

By performing such measurements, it is possible to continuously monitor the state of damage to the fuel pin.

FIG. 4 is a diagram showing an FP detection system according to a third embodiment of the present invention.

That is, the non-volatile FP capture device 46 provided between the bypass channels 6a and 6b includes a tank 47 surrounded by a shielding material such as lead (not shown), and an FP capture member 52 housed inside this tank 47. and,
A drive device 5 that drives the FP capture member 52 up and down from the outside of the tank 47 via a connecting rod 53
It consists of 4. Inside the tank 47,
Liquid sodium Q is contained therein, which is introduced into the tank 47 from the bypass channel 6a and discharged into the bypass channel 6b. This liquid sodium Q has a free liquid level X, and a cover gas S is filled above the free liquid level X inside the tank 47 . This cover gas S is supplied to a pipe 49 with a valve 48 interposed therebetween.
It is possible to supply and exhaust air into and out of the tank 47 via the tank 47. The FP capture member 52 is formed of, for example, a sintered body of stainless steel, and is immersed in liquid sodium Q present inside the tank 47.
This FP capturing member 52 is connected to the connecting rod 5 after allowing liquid sodium Q to flow inside the tank 47 for a predetermined period of time.
3 above the free liquid level X by the drive device 54. The aforementioned gamma ray detector 21 is installed at an external position of the tank 47 facing the FP capturing member 52 when it is pulled up.

Even with such a configuration, it is possible to detect gamma rays emitted from the nonvolatile FP with high precision as described above.

FIG. 5 shows the FP in the third embodiment described above.
FIG. 7 is a diagram showing a nonvolatile FP detection system according to a fourth embodiment, which includes an FP capture device 55 in which a plurality of capture members 52, connecting rods 53, and drive devices 54 are installed.

With such a configuration, the FP capture member 52 can be
Alternative lifting by drive 54 allows continuous monitoring of fuel pin failures.

6 and 7 are diagrams showing a nonvolatile FP detection system according to a fifth embodiment of the present invention.

That is, in this example, the FP capture device 60
, a plurality of FP capture members 61 are connected to a flexible belt 6
2, a pulley 64 installed inside the cover gas S to attach and drive the ring 63, and a pulley 65 similarly immersed in liquid sodium Q. It consists of The belt 62 of the ring-shaped body 63 has vertical holes 62a, as shown in FIG. pulley 64
has a plurality of drive rods 66 extending radially around its outer periphery.
This driving rod 66 is inserted into the hole 62a of the belt 62.
The annular body 63 is driven by being hooked onto the inner surface and rotated. Note that the installation position of the γ-ray detector 21 is the same as in the third embodiment described above.

The non-volatile FP detection system having such a configuration detects the FP capture member 61 by rotating the pulley 64 connected to a motor (not shown) at a constant angular velocity.
Continuous monitoring of captured FPs is possible.

Note that the present invention is not limited to the embodiments described above.

For example, the FP capturing member in the FP capturing device is not limited to stainless steel, but may be made of other metals such as Ni-based metals.

In addition, the detection method of the present invention sometimes detects the FP if the amount of γ-rays emitted from the liquid metal coolant is within a range where the amount of γ-rays from the FP captured by the capture member is small.
Even if there is some remaining amount without completely separating the capture member and liquid metal coolant, as long as the captured amount can be measured, the radiation emitted from the FP capture member including the coolant can be measured. You may also do so. Even in this case, since FP is concentrated and accumulated in the FP capture member, accurate measurement is possible. Furthermore, if the detection method of the present invention is used in combination with conventional detection methods such as the DN detection method, the γ-ray detection method, and the precipitator method, it is possible to detect everything from small-scale fractures to large-scale fractures of fuel pins. become. In this case, in the volatile FP detection system, a carbon-based substance such as graphite, which has a high C _s adsorption property, may be used as the FP capturing member. In particular, reticulated glass-like carbon has a large contact area with sodium and has a high adsorption capacity for radioactive C _s per unit volume, so it is most suitable as a trapping member.

Further, in the above embodiments, a nuclear reactor using liquid sodium as the liquid metal coolant was described, but the present invention can also be applied to a nuclear reactor using other liquid metals such as sodium potassium.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the FBR plant according to the first embodiment of the present invention, FIG. 2 is a flow sheet diagram showing the FP detection system in the plant, and FIG.
FIG. 4 is a flow sheet diagram showing an FP detection system according to a second embodiment of the present invention, FIG. 4 is a flow sheet diagram showing an FP detection system according to a third embodiment of the present invention, and FIG.
FIG. 6 is a flow sheet diagram showing an FP detection system according to a fourth embodiment of the present invention, FIG. 6 is a flow sheet diagram showing an FP detection system according to a fifth embodiment of the present invention, and FIG.
The figure is a side view showing a part of the annular body in the same embodiment. 1...Reactor vessel, 2...Reactor core, 3...Primary cooling system piping, 4...Intermediate heat exchanger, 5, 14...Pump, 6...Bypass passage, 7...Nonvolatile FP
Detection system, 11, 31 to 34, 46, 55, 60...
...FP capture device, 12, 13, 15, 17, 19,
41a to 44a, 41b to 44b, 48... valve,
16,47...tank, 18...gas cylinder, 2
0... Vacuum pump, 21... γ-ray detector, 52,
61...FP capture member, 53...connecting rod, 54...
... Drive device, 62 ... Belt, 63 ... Ring-shaped body,
64,65...pulley, Q...liquid sodium,
R, S...cover gas, X...free liquid level.

Claims (1)

[Scope of Claims] 1. After passing a part of the liquid metal coolant that has passed through the core of a nuclear reactor through a capture device housing a capture member that primarily captures non-volatile fission products, the capture member and the liquid metal coolant, and then the scale of the damage to the fuel pin is estimated by measuring the amount of radiation released by the non-volatile fission products captured by the capture member. Features fuel pin damage detection method. 2. A bypass flow path provided in the primary coolant circulation path of a nuclear reactor that uses liquid metal as the primary coolant, and a capture member that is inserted in series with this bypass flow path and captures mainly non-volatile fission products inside. a capture device containing a liquid metal; a means for causing the liquid metal to flow through the capture device for a predetermined period of time; and means for separating the non-volatile fission products from the liquid metal and captured by the capture member, A fuel pin damage detection device characterized in that the scale of damage to the fuel pin is estimated from the radiation dose. 3. Fuel pin breakage detection according to claim 2, wherein the means for separating the capture member and the liquid metal includes means for discharging the liquid metal inside the capture device. Device. 4. The means for separating the capture member and the liquid metal includes means for raising the capture member above a free surface of the liquid metal inside the capture device. The fuel pin breakage detection device according to item 2. 5. A patent characterized in that a plurality of the trapping devices are provided in parallel in the bypass channel, and the means for flowing the liquid metal for a predetermined period of time causes the liquid metal to flow through each of the trapping devices in sequence. A fuel pin breakage detection device according to claim 2. 6. The fuel pin breakage detection device according to claim 2, wherein the capture member is made of a sintered body made of stainless steel.